NCP1012: 1 W, Dual Output, Off-line Converter

DN06002/D
Design Note – DN06002/D
1 W, Dual Output, Off-line Converter
Device
Application
Input Voltage
Output Power
Topology
I/O Isolation
NCP1012
Auxiliary off-line
power supply for
appliances
85 to 270 Vac
1W
Buck/Flyback
None
Other Specifications
Output Voltage
Ripple
Nominal Current
Max Current
Min Current
Output 1
Output 2
Output 3
-5V
100 mV
100 mA
100 mA
10 mA
- 12 V
200 mV
50 mA
50 mA
0 mA
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
PFC (Yes/No)
Passive due to low input C
Minimum Efficiency
70%
Operating Temp Range
Cooling Method/Supply
Orientation
0 to +55 °C
Convection
Circuit Description
Key Features
This design is intended for low power applications where
5 V and/or 12 V may be necessary for control circuits in
appliances or similar devices in which mains isolation is
not required and low cost and simplicity are mandatory.
The topology is an off-line buck converter configured for
a 5 volt negative output with an additional negative 12
volt output derived from a secondary flyback winding on
the buck choke. The schematic notes detail how this
circuit can be converted for positive outputs if desired.
The input section uses half-wave rectification for
simplicity and allows the output common to be
referenced to the mains neutral line. An input EMI filter is
provided for conducted emissions compliance. Good
output cross regulation is achieved on the 12 V output
with the use of stacked windings in the buck choke.
Regulation feedback is achieved with a simple zener
diode and optocoupler circuit that also provides the
required offset floating for the NCP1012 controller.
September 2006, Rev. 1
Output 4
• Extremely simple and cost effective low power supply
to provide non-isolated, low voltage outputs.
• Good cross regulation due to stacked windings in the
buck choke.
• Low cost monolithic NCP1012 integrated controller
with self-biased Vcc used for buck converter.
• EMI filter on AC input for agency compliance.
• Output polarities easily reversible without component
changes.
• Over current protection.
• 2 watt capability if NCP1014 is used for U1.
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DN06002/D
Schematic
1
D2
L2
L1
R1
15
2W
AC input
90 - 285Vac
1 mH
C1
100nf
"X"
1
D1
MRA4007T3
MURS160T3
R4
1K
W2
4
6
C7
330uF
16V
- 12 Vdc
@ 50 mA
C8
0.1uf
50V
3
W1
3.5 mH
- 5 Vdc
@ 100 mA
C6
C2
D3
MURS160T3
10 uF
400V
C5
NCP1012
(SOT-223)
3
MMSZ5229B
2
4
1
U2
1
C4
C3
47uF+
16V
NOTES:
Com
R5
(Vtrim)
0 ohm
U1
4
0.1uf
50V
470 uF
6.3 Vdc
470pF
3
opto
R2
47
Z1
4.3V
R3
220
2
1. Crossed lines on schematic are not connected.
2. U1 should have ground tab (pin 4) soldered to expanded ground plane area for good heatsinking (SOT-223 recommended package).
3. U2 is Vishay H11A817A optocoupler or equivalent
4. R1 provides inrush limiting at turn-on (optional).
5. C5 capacitance value dependent on max Vout ripple; 470 uF min recommended.
6. L1 is Cooper/Bussmann UP2B-102R inductor (Uni-Pac series - 1 mH, 0.3 A) or similar.
7. L2 is P18/11/I ferrite core (1811 pot core without hole) on 6 pin pc mount bobbin;
W1 is 92 turns of #32HN (0.25 mm dia) magnet wire wound over 4 layers (23 turns per layer).
W2 is 115 turns of #32 HN magnet wire woundover 5 layers (23 turns per layer).
Core should be gapped to give an inductance of 3.4 to 3.6 mH across W1.
8. R5 is option voltage trim resistor - increasing resistance increases Vout.
9. For positive outputs: reverse diodes D1, D2, and D3; apply dc input to pin 3 of U1 and
output will be on pin 4; reverse voltage sensing so cathode of zener goes to 5V output
and pin 2 of U2 (opto) goes to output common; reverse polarity of input and output
caps C2, C5 and C7.
NCP1012 1 Watt, Dual Output Converter
ON Semiconductor Applications Group
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© 2006 ON Semiconductor.
Disclaimer: ON Semiconductor is providing this design note “AS IS” and does not assume any liability arising from its use; nor
does ON Semiconductor convey any license to its or any third party’s intellectual property rights. This document is provided only to
assist customers in evaluation of the referenced circuit implementation and the recipient assumes all liability and risk associated
with its use, including, but not limited to, compliance with all regulatory standards. ON Semiconductor may change any of its
products at any time, without notice.
Design note created by Frank Cathell, e-mail: [email protected]
September 2006, Rev. 1
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